Hydraulic actuator

ABSTRACT

A hydraulic actuator comprising a fluid-containing cylinder with a cover incorporating a bore in which a plunger is displaceably journalled with a leak-proof sealing, said plunger being connected rigidly with a plunger rod which is connected directly and pivotably with a lever which is journalled to be pivotable relative to the cylinder through a predetermined angle of rotation, whereby to impress a rocking movement on the plunger rod during axial displacement of the plunger. The length of the bore is at least equal to the maximum axial travel of the plunger and the diameter of the bore differs at every point and in any position from that of the plunger by an amount exceeding twice the possible lateral movement of the plunger at that point caused by said rocking movement of the plunger rod, the leak-proof sealing between the plunger and the bore being effected by an Oring, a diameter of which forms an axis of rotation for the plunger rod.

United States Patent [191 Christiansen Mar. 25, 1975 HYDRAULIC ACTUATOR [75] Inventor: Palle Hein Christiansen, Naestved,

Denmark [73] Assignee: Nordisk Ventilator Co., A/S,

Naestved, Denmark 22 Filed: Aug. 15, 1973 211 App]. No.: 388,667

[30] Foreign Application Priority Data s & 1

Primary Examiner-Martin P. Schwadron Assistant Examiner-J1. Burks, Sr.

Attorney, Agent, or Firm-Sughrue, Rothwell, Mion, Zinn & Macpeak [57] ABSTRACT A hydraulic actuator comprising a fluid-containing cylinder with a cover incorporating a bore in which a ,plunger is displaceably journalled with a leak-proof s'aiingg s aid plunger beiii g c onnecte d rigidly with a plunger rod which is connected directly and pivotably with a lever which is journalled to be pivotable relative to the cylinder through a predetermined angle of rotation, whereby to impress a rocking movement on the plunger rod during axial displacement of the plunger. The length of the bore is at least equal to the maximum axial travel of the plunger and the diameter of the bore differs at every point and in any position from that of the plunger by an amount exceeding twice the possible lateral movement of the plunger at that point caused by said rocking movement of the plunger rod, the leak-proof sealing between the plunger and the bore being effected by an O-ring, a diameter of which forms an axis of rotation for the plunger rod.

3 Claims, 2 Drawing Figures HYDRAULIC ACTUATOR The present invention relates to a hydraulic actuator consisting of a cylinder with a displaceable plunger passing leak-proof through a bore in a cover on the cylinder, a plunger rod connected rigidly to the plunger being coupled to a lever which is pivotable relative to the cylinder through a predetermined angle of rotation.

Actuators of this kind operate in such a way that a variation in the volume of fluid contained in the cylinder results in a corresponding, oppositely-directed variation in the volume of the part of the plunger located in the fluid and thus in a corresponding displacement of the plunger. The variation in the volume of the fluid can be caused by a variation in temperature or by the supply or removal, respectively, of an additional quantity of fluid through a tube by means of a control device which may be a temperature sensor or a control cylin' der with a plunger mounted therein.

In prior art actuators of the kind described the plunger is controlled in such a way that it performs together with the plunger rod a purely axial movement which necessitates that the connection between the plunger rod and the lever posseses a mobility which may be obtained by means of an additional lever or by engagement between a pin on one of said two members and an oblong hole in the other member. In both instances this results in a certain amount of play in the connection so that rocking movement of the lever does not accurately accompany the displacement of the plunger rod.

According to the invention a hydraulic actuator is provided, comprising a fluid-containing cylinder, a cover fixed at one end of said cylinder and incorporating a bore, a plunger passing with a leak-proof sealing through said bore and being displaceable between two extreme positions by varying the fluid volume in the cylinder, a plunger rod connected rigidly to said plunger and a lever coupled to said plunger rod and being journalled to be pivotable relative to the cylinder through a predetermined angle of rotation, wherein the improvement comprises that the lever is connected directly and pivotably to the plunger rod and isjournalled at a point of rotation stationary relative to the cylinder, whereby to impress a rocking movement on the plunger rod during axial displacement of the plunger, the length of the bore being at least equal to the maximum axial travel of the plunger and the diameter of the bore differing at every point and in any position from that of the plunger by an amount exceeding twice the possible lateral movement of the plunger at that point caused by said rocking movement the plunger rod, the leakproof sealing between the bore and the plunger comprising an O-ring, a diameter of which forms an axis of rotation for the plunger rod.

As a result hereof a simpler structure is obtained than in prior art actuators in which an additional lever is employed and the transmission of the movement from the plunger rod to the lever will be more accurate and free of play than in any of the above-mentioned prior art de- Moreover, it has to be emphasized that tests simulating long-term operation have shown that it is possible to achieve a very long service life with reliable sealing despite the fact that the O-ring, in the course of the movement, in addition to sliding in the axial direction, is subjected to a certain amount of rocking, because the plunger, during the axial movement, simultaneously performs a rocking movement around a diameter in the O-ring.

In a particular embodiment of the invention this rocking movement can be reduced to the maximum possible extent by arranging the axis of the plunger to be approximately parallel to the axis of the bore in two positions, one of which lies approximately midway between one extreme position of the plunger and a central position between the two extreme positions and the other approximately midway between the central position of the plunger and the other extreme position.

In the following the invention is explained in greater detail with reference to the accompanying drawings, in which FIG. ll shows an embodiment of an actuator according to the invention constructed as a thermostat, and

FIG. 2 shows a portion of a modified embodiment,

The actuator illustrated in FIG. 1 consists of a cylinder 1 with a displacing plunger 2 passing through a bore 3 in the cover of the cylinder which, in the embodiment shown, is constructed as a sleeve 4 This sleeve 4 is axially displaceable in a bore in a top flange 5 which is rigidly connected to cylinder 1, a sealing being provided between sleeve 4 and top flange 5 by means of an O- ring 6. The movement of the sleeve in a downward direction in the cylinder is restricted by means of a flange 7, while the movement in the opposite direction is counteracted by a plurality of Belleville springs 8 surrounding the plunger rod 9, which is integral with plunger 2, said Belleville springs :B being clamped between flange '7 0n sleeve 4 and a top piece 10 which is rigidly connected by means of stay bolts 11 to flange 5 and is spaced therefrom by means of a cylindrical cover 12 surrounding Belleville springs 8, said cover furthermore controlling the springs and protecting them against the penetration of dirt and other extraneous influences.

On the upper side of top piece It) and upright support 13 is mounted, at the upper end of which a lever 14 is pivotably journalled around a pin 15. In addition, lever 14 is pivotably connected by means of a pin 16 to the upper end of plunger rod 9.

Plunger rod 9 is passed unimpededly through an aperture 17 in top piece 10 and is surrounded by a sleeve 18 which is secured to the plunger by means of a pin a rivet 19. The height of sleeve 18 is less than the internal distance between the upper side of sleeve 4 and the lower side of top piece 10 and, in the lowest position of plunger 2 the sleeve 18 is in abutment against sleeve 4, whereas, in the upper position of plunger 2, it is in abutment against top piece 10 and thus serves to determine the limits of travel of plunger 2. Plunger 2 is sealed against the wall of bore 3 in sleeve 4 by means of an O-ring 20 which is retained in a circumferential groove in plunger 2. The length of travel of plunger 2 determined by the sleeve has thus to be, at the most, equal to the axial length of bore 3 reduced by the thickness of O-ring 20.

In the embodiment shown, cylinder 1 is completely closed by a bottom portion 21. It is filled with a fluid,

e.g. glycerine, and the actuator is consequently capable of acting as a thermostat in which cylinder 1 simultaneously as a temperature sensor. By heating cylinder 1 and, thereby, the liquid contained therein, the volume of the fluid is increased and plunger 2 is displaced in a corresponing manner outof the cylinder thereby executing an axial movement in a upward direction.

In order to secure return movement the plunger is provided with an extension 22 projecting down into the cylinder and carrying, at its lower end, a sleeve 23, said extension being furthermore surrounded by a return spring 24 which is in contact with said sleeve 23 as well as sleeve 4.

Instead of being completely closed, the cylinder can be connected with an independent temperature sensor or another hydraulic operating means via a tube 25 such as indicated in dotted lines in FIG. 1.

Lever 14 may be connected, for example, to a damper in a ventilation system for adjusting said damper in dependence on temperature or to any other element that is to be controlled by hydraulic actuation.

In prior art hydraulic actuators of the kind described the travel of the plunger is a purely axial movement and since the movement of lever 14 is a circular movement, a linkage is consequently required between lever 14 and plunger rod 9, for instance, by means of a lever or by engagement of pin 16 with an oblong hole in one of the two members.

According to the invention, such a linkage is not present, but plunger 2 is, on both sides of the'O-ring 20, proportioned with an outer diameter being so much smaller than the diameter of bore 3 that the rocking movement necessitated by the movement of pin .16 along a circular path can be superposed upon the axial movement of the plunger. Thereby, both a simplification of the construction and a greater accuracy in the adjustment are achieved.

During normal movement of the plunger, flange 7 of sleeve 4 will constatly abut against top flange 5 due to the spring tension stemming from Belleville spring 8. Therefore, bore 3 may, in principle, extend in a fixed top piece. However, by employing the construction shown it is achieved that an expansion of the fluid in cylinder 1 beyond the volume corresponding to the upper limit position of the plunger determined by sleeve 18 will result in an axial displacement of sleeve 4 against the action of springs 8 so that overloading will not give rise to destruction of the actuator.

The rocking movement performed by the plunger during the axial movement takes place, generally speaking, around an axis in the plane of O-ring 20 through the centre therof for which reason oppositely directed torsional stresses will appear in the two halves of the O-ring. In order to restrict the rocking of the plunger and, thereby, reduce these torsional influences, it is expedient for the axis of plunger 2 to coincide with the axis of bore 3 in two positions, one of which is approximately midway between one extreme position and the centre position of the plunger and the other approximately midway between the centre position of the plunger and the other extreme position.

FIG. 2 shows a modified construction of one portion of the actuator illustrated in FIG. 1 which essentailly only differs from the construction shown in FIG. 1 in that O-ring 20 is retained in a groove in a sleeve 27 cor- Plunger 28 is cylindrical and has a uniform diameter throughout its length, while bore 29 in sleeve 27 diverges conically to both sides of O-ring 20 so that the necessary play is obtained thereby for the rotary movement of the plunger during the axial movement.

In order to achieve the requisite sealing, it is necessary for the surfaces sliding relative to the O-ring to be ground surfaces. This means that the inner wall of bore 3 in FIG. 1 has to be ground, while in FIG. 2 it is the plunger which has to have a ground surface.

When bore 3 is present in a sleeve 4 as in the embodiment shown in FIG. 1, where a sealing must also be present on the outer side of the sleeve, it is advantageous for the O-ring to be retained on the plunger because in this case it is only necessary for a single member, i.e., sleeve 4, to have ground surfaces. If use is not made of such a displaceable sleeve, but the O-ring is located in a top piece connected rigidly to cylinder 1 so that sealing has only to be present at one point, the construction shown in FIG. 2, in which it is the plunger which has to be constructed with a ground surface, will often be more advantageous.

Iclaim:

1. In a hydraulic actuator having a fluid-containing cylinder, a cover fixed at one end of said'cylinder and incorporating a bore, a plunger passing with a leakproof sealing through said bore and being displaceable between two extreme positions by varying the fluid volume in the cylinder, a plunger rod connected rigidly to said plunger and a lever coupled to said plunger rod and being journalled to be pivotable relative to the cylinder through a predetermined angle of rotation, wherein the improvement comprises a. the length of the bore is at least equal to the maximum axial travel of the plunger;

b. the diameter of the bore differs at every point and in any position from that of the plunger by an amount exceeding twice the possible lateral movement of the plunger at that point caused by a rocking movement of the plunger rod; and

c. the leakproof sealing between the bore and the plunger is effected by an O-ring, a diameter of which forms an axis of rotation for the plunger rod, thereby enabling a rocking movement on the plunger rod during axial displacement of the plunger and the lever to be connected directly and pivotably to the plunger rod and journalled at a point of rotation stationary relative to the cylinder.

2. A hydraulic actuator as claimed in claim 1, wherein the mutual arrangement of the plunger, the plunger rod and the lever relative to the bore is such that the axis of the plunger is parallel to that of the bore in either of two positions, one of which lies substantially midway between one of said extreme positions and a central position of the plunger between the two extreme positions, whereas the other of said two positions lies substantially midway between said central position and the other extreme position.

3. A hydraulic actuator as claimed in claim I wherein the plunger is provided with an annnular groove to ac- 

1. In a hydraulic actuator having a fluid-containing cylinder, a cover fixed at one end of said cylinder and incorporating a bore, a plunger passing with a leakproof sealing through said bore and being displaceable between two extreme positions by varying the fluid volume in the cylinder, a plunger rod connected rigidly to said plunger and a lever coupled to said plunger rod and being journalled to be pivotable relative to the cylinder through a predetermined angle of rotation, wherein the improvement comprises a. the length of the bore is at least equal to the maximum axial travel of the plunger; b. the diameter of the bore differs at every point and in any position from that of the plunger by an amount exceeding twice the possible lateral movement of the plunger at that point caused by a rocking movement of the plunger rod; and c. the leakproof sealing between the bore and the plunger is effected by an O-ring, a diameter of which forms an axis of rotation for the plunger rod, thereby enabling a rocking movement on the plunger rod during axial displacement of the plunger and the lever to be connected directly and pivotably to the plunger rod and journalled at a point of rotation stationary relative to the cylinder.
 2. A hydraulic actuator as claimed in claim 1, wherein the mutual arrangement of the plunger, the plunger rod and the lever relative to the bore is such that the axis of the plunger is parallel to that of the bore in either of two positions, one of which lies substantially midway between one of said extreme positions and a central position of the plunger between the two extreme positions, whereas the other of said two positions lies substantially midway between said central position and the other extreme position.
 3. A hydraulic actuator as claimed in claim 1 wherein the plunger is provided with an annnular groove to accomodate said O-ring. 